Electrically conductive fillers

One single property of filler - electric conductivity - affects many properties of the final products. These properties include electric insulation, conductivity, superconductivity, EMI shielding, ESD protection, dirt pickup, static decay, antistatic properties, electrocatafysis, ionic conductivity, photoconductivity, electromechanical properties, thermo-electric conductivity, electric heating, paintability, biocompati-bilify, etc. Possession of one of these properties in a polymer can make it useful in industiy and eveiyday use. Examples are given in Chapter 19. Here, the electrical... 

The last property named greatly influences stmctural distortion that can occur in welding. The electrical conductivity of a material is important in any welding process where base or filler metal is part of the welding electrical circuit. 

Electrically conductive mbber (13) can be achieved by incorporation of conductive fillers, eg, use of carbon or metal powders. These mbbers exhibit volume resistivities as low as lO " H-cm. Apphcations include use in dissipation of static charge and in conductive bridging between dissimilar electronic materials under harsh operating conditions. 

For many electronic and electrical appHcations, electrically conductive resias are required. Most polymeric resias exhibit high levels of electrical resistivity. Conductivity can be improved, however, by the judicious use of fillers eg, in epoxy, silver (in either flake or powdered form) is used as a filler. Sometimes other fillers such as copper are also used, but result in reduced efficiency. The popularity of silver is due to the absence of the oxide layer formation, which imparts electrical insulating characteristics. Consequently, metallic fibers such as aluminum are rarely considered for this appHcation. 

Reiaforced plastics may also iaclude fillers (qv), which are iaexpeasive materials such as calcium carboaate used to displace resia and reduce cost curing agents (catalysts), promoters, inhibitors, and accelerators, which affect thermosetting resia cure colorants release agents (qv) to faciUtate removal from the mold and other additives which can impart a wide variety of properties to the finished part, such as fire resistance, electrical conductivity, static dissipation, and ultraviolet resistance. 

Carbon Blacks. The high electrical conductivity of carbon black is utili2ed where its color is not objectionable and its reinforcing action is used (see Fillers Composites). Carbon black increases the electrical conductance of the polymer to which it is added, and therefore its effectiveness does not depend on moisture absorption (see Carbon, carbon black). 

This article addresses the synthesis, properties, and appHcations of redox dopable electronically conducting polymers and presents an overview of the field, drawing on specific examples to illustrate general concepts. There have been a number of excellent review articles (1—13). Metal particle-filled polymers, where electrical conductivity is the result of percolation of conducting filler particles in an insulating matrix (14) and ionically conducting polymers, where charge-transport is the result of the motion of ions and is thus a problem of mass transport (15), are not discussed. 

During the past 30 years considerable research has been undertaken that has led to electrically conducting polymers that do not rely on the use of fillers, the so-called intrinsically conductive polymers. Such polymers depend on the presence of particles which can transport or carry an electric charge. Two types may be distinguished ... 

The main feature of the CPCM is a drastic difference between electric conductivity of a polymer matrix and the filler reaching a factor of 1024 in terms of resistivity (Fig. 1). There is no such difference in relation to any other physical property of com-... 

Quite naturally, novel techniques for manufacturing composite materials are in principal rare. The polymerization filling worked out at the Chemical Physics Institute of the USSR Academy of Sciences is an example of such techniques [49-51], The essence of the technique lies in that monomer polymerization takes place directly on the filler surface, i.e. a composite material is formed in the polymer forming stage which excludes the necessity of mixing constituents of a composite material. Practically, any material may be used as a filler the use of conducting fillers makes it possible to obtain a composite material having electrical conductance. The material thus obtained in the form of a powder can be processed by traditional methods, with polymers of many types (polyolefins, polyvinyl chloride, elastomers, etc.) used as a matrix. 

Filler or Reinforcement Chcmicul Resistance i 8 u i i Electrical Insulation Impact Strength Tensile Strength Dimensional Stability Stiffness Hardness Lubricity Electrical Conductivity Thermal Conductivity 1 8 C s TS 1 X I I h 11... 

Incorporating reinforcing particles that respond to a magnetic field is important with regard to aligning the particles to improve mechanical properties anisotropically [223-226]. In related work, some in-situ techniques have been used to generate electrically conducting fillers such as polyaniline within an elastomeric material [227],... 

Electrical conduction ceramics, 5 585-587 glasses, 5 592-593 Electrical conductivity. See also Conductivity of foams, 12 11 fillers and, 10 434 silver, 22 639... 

Fig. 6.7 (a) The variation of electrical conductivity of PVA-EG hybrid with increasing graphene content. Inset shows the dependence of dielectric constant for the hybrid, (b) The variation of conductivity of the polystyrene-graphene hybrid with filler content. Inset shows the four probe setup for in-plane and transverse measurements and the computed distributions of the current density for in-plane condition (reference [8]). 

Similar metal sheets have also been used as DLs in the cathode of PEMFCs. Wilkinson et al. [37,38] presented the idea of using fluid distribution layers made out of metal meshes with electrically conductive fillers inside the holes of the meshes. A very similar idea was also presented by Fiamada and Nakato [39]. Eosfeld and Eleven [40] presented another example of fuel cells that use metal meshes as diffusion layers along with metal FF plates. 

In addition to graphite, carbon filler has also been added in composite plates. The major difference between graphite and carbon fillers in the composite plate is that the latter is less electrically conductive but is cheaper than... 

Overall, as mentioned previously, the major challenge in composite plates is how to maintain the best balance between electrical conductivity and mechanical properties. This is mainly influenced by the ratio between the fillers and matrix. Regarding the electrical conductivity, well designed and manufactured composite materials show performance comparable to that of graphite. For example, the bulk electrical conductivity of a well designed and fabricated composite can reach 300 S cm i, close to that of the graphite [21]. 

However, if the volume ratio between the filler and the matrix is too high, the composite can become brittle, similar to dense graphite, and the advantage of composite plates in cost reduction will not exist. Hence, the normal composite plate contains about 50-80% fillers so as to have balanced electrical conductivity and mechanical properties with the accepted low cost. 

In addition to the amount of filler content, the shape, size and size distribution, surface wettability, interface bonding, and compatibility with the matrix resin of the filler can all influence electrical conductivity, mechanical properties, and other performance characteristics of the composite plates. As mentioned previously, to achieve higher electrical conductivity, the conductive graphite or carbon fillers must form an interconnected or percolated network in the dielectrical matrix like that in GrafTech plates. The interface bonding and compatibility between... 

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